Payne packaged AC or rooftop unit displays F2; unit may shut down during operation.

Safety: Turn off all power to the unit before opening the blower or control compartment.

• 1. Find the supply sensor: The supply air thermistor is typically mounted in the discharge air plenum or duct just downstream of the evaporator coil.
• 2. Check mounting and wiring: Ensure the sensor is securely mounted in the airstream and that its wires are intact and firmly connected to the control board.
• 3. Clean dust/debris: If the sensor is coated with dust, gently clean it with a soft brush or compressed air.
• 4. Power cycle: Restore power and test operation. If F2 returns, the sensor likely needs replacement.
• 5. Professional verification: A technician can ohm-test the thermistor and compare readings to Payne's resistance/temperature chart to confirm failure.